Protective covering for molten metal



United States Patent US. Cl. 7596 2 Claims ABSTRACT OF THE DISCLOSURE Avery finely divided protective cover for molten metals, produced fromeasily handleable granules of a protective material such as carbon and amaterial such as vermiculite which, under the action of the heat of themolten metal, intumesces to disintegrate the granules.

This invention relates to the casting of metals and more particularly tothe provision on molten metal of a protective covering and to newcompositions for use in the provision of such protective coverings.

It is a well-known practice to apply powdered materials to the surfaceof molten metal at various stages in its handling for such purposes asfluxing, protection and heatinsulation. The practice is common, forexample, in han dling non-ferrous metals where the molten metal in theladle is provided with a protective covering. Such a layer, which may beof a carbonaceous character, serves a number of useful purposes; inparticular it serves as a heatinsulating layer to delay the loss of heatfrom the surface metal and it provides over the metal and atmosphere ofa chemically reducing nature so that surface oxidation of the metal isreduced or curtailed.

In the continuous or semi-continuous casting of molten non-ferrous metalthe layer is commonly extended to cover the metal in the launder and inthe casting die and it serves an additional purpose as a lubricant forthe continuously cast billet.

The carbonaceous materials commonly employed for the foregoing purposesinclude such materials as lamp black, carbon black, micronised graphiteand similar materials which are employed in a very fine state ofsubdivision. It accordingly arises that in the provision of thecovering, and later if the covering is disturbed, there are formedclouds of black dust which are both inconvenient and unpleasant to theoperatives. An attempt to overcome this objection by granulating thecarbonaceous material with the aid of a conventional binding agent, e.g.a gum, dextrin or like material, proves unsatisfactory because thegranules tend to retain their granular structure and theirheat-insulating properties, and particularly their lubricatingproperties, are very largely lost.

It is an object of the present invention to provide an improvement inthe methods referred to above, and to provide new materials for suchuses, whereby the covering material though initially of a granularcharacter is converted in use to a finely divided powder material.

According to the present invention there is provided a granularcomposition for use in the provision of a covering for molten metalwhich comprises granules of surfacetreating materials as known per se,each granule comprising very finely divided treating material and asubstance which on heating will intumesce or generate a gas. When such acomposition is put to use the initial granular form of the materialavoids the formation of clouds of powdered material. On the other hand,by reason of the presence of the gas-generating or intumescent substancethe granules, under the influence of the heat of the molten 3,516,821Patented June 23, 1970 metal become disintegrated to provide thepulverulent material in the highly desirable very finely dividedcondition.

The compositions may contain a conventional binder such as dextrinprovided that the binding effect of the binder is not so great as toprevent the disintegration effect of the gas generated by thegas-generating additive or of the intumescence of the intumescentadditive.

Any substance which, on heating to the temperature of the molten metal,will generate a gas, preferably in large volume, may be employed and itis possible to work with the aid of water alone as the additive presentin the granules. In this case the resulting steam affords thedisintegrating effect although, for some metals, the atmosphere createdis undesirable. Therefore, it is generally preferable to employ drychemical substances which volatilise or decompose to generate gaseswhich do not contain constituents deleterious to the molten metal.Particularly useful materials are the metal carbonates, e.g. calciumcarbonate, urea or any of the gas-generating substances known per se foruse as blowing agents in the foamed plastics industry e.g. bicarbonates,ammonium nitrate, azo and nitroso compounds. The gas-generating agentshould be selected with regard to the desirability of maintaining asuitable atmosphere over the molten metal when the granular compositionis put to use.

Suitable additives which intumesce on heating, i.e. which swell orexpand, and which may be used in the present invention include materialswhich exfoliate on heating such as vermiculite and materials which swellsuch as perlite and powdered sodium silicate. The invention is not,however limited to these substances, and any substance of which theparticles will expand substantially on heating may usefully be employed.

The proportion of the gas-generating or intumescent additive in thegranules will vary with the particular substance and with the particularsubstance and with the degree of explosive effect sought to be obtainedby the gas-generation or intumescence. Generally, in the manufacture ofthe granular composition, a proportion of gasgenerating or intumescentagent not exceeding 50% will be used, the quantity necessary forsatisfactory results usually being up to 15% e.g. 0.5 to 10% by weight.

Other materials may be included in the compositions of the presentinvention for specific purposes. For example it is sometimes desirableto include a slag-forming agent, e.g. a fluoride such as fluorspar.

The following examples will serve to illustrate the invention:

EXAMPLE I A mixture of 50 parts by weight of carbon black and 5 parts byweight of finely divded chalk was granulated with the aid of 50 parts byweight of water. The granules obtained were dried and applied to thesurface of molten copper in a ladle.

It was observed that the granules gently disintegrated to form a layerof very finely divided carbon over the surface of the molten copperwithout generating clouds of black dust and the resulting cover wasfound to have heat-insulating properties similar to those of a layer ofcarbon black of equal thickness conventionally applied.

EXAMPLE II A mixture of 92 parts by weight of ground charcoal (graded-16+150 B.S.S. mesh). 8 parts by weight of unexfoliated vermiculite(graded 22+60 B.S.S. mesh) and 3 parts by weight of pregelatinisedstarch was mixed with an equal weight of water and granulated, e.g. bypassage through a conventional meat-mincing machine. The granulatedproduct was dried at about C., care being taken not to allow thetemperature to exceed C.

The granules were applied to the surface of molten copper as in Example1 and analogous results were obtained.

The present invention includes both the new compositions hereindescribed and the method of protecting the surface of molten metal bythe use thereof, also as herein described.

I claim as my invention:

1. In a treatment of molten metal wherein there is applied to thesurface of the molten metal a very finely divided particulate protectivecovering therefor, the step which comprises adding to the molten metal,to generate such covering, granules each containing a portion of veryfinely divided carbon, and as a substance which on heating willintumesce, vermiculate, whereby the granules are disintegrated by theheating supplied by the molten metal, said vermiculate being of a sizesuflicient to pass through a 22 mesh but be retained on a 60 mesh.

2. A protective material for application to the surface of a moltenmetal, the said protective material being in a granular form in whicheach granule comprises very finely divided carbon and, as a substancewhich on heating will intumesce to thereby disintegrate the granule,vermiculate, said vermiculate being of a size sufiicient to pass througha 22 mesh but be retained on a 60 mesh.

5 References Cited UNITED STATES PATENTS 324,505 8/1885 Walton 7596 X354,995 12/1886 Wheeler 7596 X 1,750,751 3/1930 Geyer.

2,497,745 2/ 1950 Stohr 7594 X 3,340,045 9/1967 Colwell 7594 X FOREIGNPATENTS 15 820,137 9/1959 Great Britain.

HENRY W. TARRINGTON II, Primary Examiner US. Cl. X.R. 93, 94

P040150 UNITED STATES PATENT OFFICE (569) CERTIFICATE OF CORRECTIONPatent No. 3, 516 821 Dated June 23, 1970 Inventor) MAX GERHARD NEU Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

r- In the Heading, column 1, line 4, after the word England, insert thewords -assignor to Foseco International Limited, Birmingham, England, acompany of Great Britain.

31 mama amen 001201970 6m) WILLIAM r. sum. :12. Attest: Commissioner ofPatents Edward M. Fletcher, 11:

Attesting Officer

